Augmented reality head mountable displays display augmented reality images on display surfaces typically mounted on a frame and positioned near each of a user's eyes. Because the display surfaces are located near the user's eyes, such displays are also referred to as near eye displays. One particular type of near eye display is a see through display, which allows the user to view the real world through the display surfaces. Thus, the user sees a combination of the real world and augmented reality images when looking through the display surfaces.
When viewing real world objects, the user's eyes rotate so that the views from the left and right eyes converge at a fixed distance in space corresponding to the location of the real world object being viewed. This distance is referred to herein as the vergence distance. The user focuses on real world objects at the vergence distance through changes in the pupil aperture size.
Augmented reality images displayed to a user via a near eye see through head mountable display appear to be in focus at a distance defined by the optics of the display system. If the distance at which an augmented reality image appears to be in focus matches the vergence distance where the user's eyes are currently focusing on a real world object viewed through the display, the user will simultaneously perceive the real object and augmented reality image to be in focus. However, if the vergence distance does not match the distance at which the augmented reality image appears to be in focus, the augmented reality image may appear blurry or unnaturally proportioned with respect to the real world objects being viewed.
In some augmented reality head mountable displays, the distance from the user's eyes at which the augmented reality images appear to be in focus is fixed. As a result, when the user is viewing different objects in the real world at different distances from the user's eyes, the augmented reality images may appear out of focus at some distances. Displaying augmented reality images to the user that are out of focus at some distances may result in user discomfort when the user tries to simultaneously view augmented reality images and real world images that are in focus at different distances.
Some augmented reality head mountable displays utilize varifocal mirrors to rapidly vary the distance at which augmented reality images appear in focus by vibrating the surface of the mirror on which the images are viewed. The rate of vibration is faster than the human eye can focus on a specific distance, which is intended to increase the depth of field at which the augmented reality images are perceived to be in focus. However, such vibration is not based on the vergence distance of the user's eyes and can result in a mismatch between the vergence distance and the distance(s) at which the augmented reality images appear to be in focus. Another problem with some augmented reality head mountable displays that use varifocal mirrors is that the displays are not see through displays and thus require complex optics to place the virtual and real world images in front of the user's eyes. Still another problem with some augmented reality head mountable displays is that they present a narrow field of view to the user. For example, some near eye see through displays present a field of view of about 30 degrees for each eye.
Accordingly, in light of these difficulties, there exists a need for a wide field of field of view head mountable display with distance accommodation.